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Mimosa (Mimosa pigra) threatens large parts of the
Northern Territory including World Heritage-listed
Kakadu National Park. It prevents indigenous people
from accessing their country and $0.5 million is
spent every year just to keep it out of Kakadu.
Photograph by Colin Wilson.

One of the best laws in the Western world on ecological protection, Australia's Environment Protection and Biodiversity Conservation Act (1999), is not being used when it comes to the widespread threat posed to the environment by foreign plants, according to Dr Rachel McFadyen, CEO of the Cooperative Research Centre for Australian Weed Management.

Dr McFadyen said at the Biodiversity Extinction Crisis Conference in Sydney that the EPBC Act allowed action once a 'key threatening process' had been identified and declared. Examples of official recognition so far included the rabbit, fox, goat, feral cats, the root rot-fungus phytophthera, long-line fishing, climate change and cane toads.

However, not a single invasive plant had been listed as posing a significant threat, Dr McFadyen said.

'Yet we have plants from Central America forming one-species stands over thousands of hectares, totally displacing the native flora and fauna. Mimosa even prevents indigenous people from accessing their country, and Kakadu National Park spends $0.5 million every year just to keep it out, they see it as such a threat', she said.

Mesquite, olive hymenachne, lantana, blackberry and bitou bush are all recognised as Weeds of National Significance under other federal measures. All are very clearly rampant invaders of valuable natural ecosystems, but none are listed under the EPBC Act, Dr McFadyen said.

'One of the worst offenders is the African gamba grass, still being promoted and planted as pasture for cattle in the north', Dr McFadyen said.

'This is a monster of a grass that can grow over four metres high. It seeds prolifically and invades surrounding woodland savannah country - and when it burns the heat is just too much for the eucalypts, which die.'

'The result is goodbye eucalypt woodland with its complex of associated plants, birds and other animals, and hello African grassland which allows very few of these species a look in', she said.

'It does make me wonder what a foreign plant has to do to get attention from conservationists. I sometimes think we are up against a prevailing misinformed mindset that sees all green plants as essentially the same - as passive, friendly and just part of nature.'

'Try telling that to a landowner or park manager battling rubber vine, cat's claw creeper, gorse, broom, boneseed, bridal creeper or any of the dozens of highly invasive foreign plants that chew up huge amounts of time and money on a daily basis around Australia.'

Dr McFadyen said that recent research was beginning to paint a picture of how threatening weeds were to native plants and animals.

'There has been a serious underinvestment in this ecological impact research for many years, but we are now starting to get a better handle on it. We now know, for example, that weeds are a significant threat to over one third of endangered species nationally, including within 13 World Heritage Areas - and our international responsibilities to protect them are very clear', she said.

'In NSW, where the Weeds CRC commissioned work in 2006, weeds are known to be a direct threat to almost half of the threatened species listed for that state. We know, for example, that the habitat of the northern corroboree frog is directly threatened by blackberry invasion, and the native rice flower by bitou bush and lantana.'

The lack of research and data for individual species makes it difficult to pin-point specific threats with the precision that scientists would like, Dr McFadyen said. But we do understand the sorts of changes that weeds cause, and how these tend to affect local flora and fauna.

'We know, for example, that nectar-feeding birds such as lorikeets will abandon bushland when their food source is displaced by weeds that do not produce nectar.'

That's something that's obvious, but there's a lot more going on.'

The reality is that such displacement of native plants, birds and other animals is happening quietly on a vast scale across the continent, as weeds gradually make their environment less attractive and less supportive, Dr McFadyen said. Climate change will also add real pressure.

'The really big weakness we have as custodians of this natural heritage', Dr McFadyen said, 'is that too often we only address the biodiversity issue at points or times of crisis, when certain species are threatened with imminent extinction. That is reflected in the language we use', she said.

In the meantime, Dr McFadyen said, we seem to be largely unaware of the immense changes we have caused to this heritage, and which continues to degrade wherever weeds get the upper hand.

'In fact, now that wholesale land clearing has largely stopped, weeds constitute the number one threat to biodiversity. This is a widely observed phenomenon around the world.'

The end point of this very long-term process of weed invasion is hard to predict, but it is not likely to be good news for our native flora and fauna, Dr McFadyen said.

'We need to understand this much better and plan and act accordingly, not carry on as if all green plants are equal. The nation is not a Peter Andrews production system.'